I don't know of any examples of questions of the form "ona li seli?", except for some mistakes I do from time to time. Even though the Official Book doesn't contain these examples, I would understand (and possibily use) them in a dialog like this:

Although no one likes to talk about them, unmarked questions of the 'ona li seli?' form occur from time to time. The problem with them is that, since we don't know anything about tp spoken sentence contours, we don't know what the open question sounds like. Anglophones, of course, have that rising-toward-resolution pitch glide (or did, until it became the teenies normal sentence ending). Other languages have other patterns, including none, for languages which are always explicit about questions. But the question mark solves this problem in written tp. And one form of this is not only common but fundamental, the 'anu' choice question: 'sina wile e telo pimeja anu telo lipu?', which is overtly indistinguishable from a declaration about your possible wants. (This is fundamental because it underlies 'x ala x' -- originally 'x ala anu x' -- and, more obviously, S anu seme?', whose analysis is rather complex.)

The problem with 'seme anu S?' is that the 'seme anu' is likely to get caught up with the subject of the S, suggesting that the choice was not "yes" and "no" but about what the proper subject of the S was. To be sure, the claim that 'x ala x' and 'S anu seme' are equivalent is fairly clearly wrong anyhow. The first allows conventionally only the answers '(x) ala' and 'x', whereas the second allows almost anything relevant (broadly interpreted), typically alternate suggestions (which might come up after an 'ala' by way of explanation or suggestions how to proceed). The 'seme' seems, in most cases. to match S as its category and so allow -- in two steps -- for a totally new sentence directly.

Its not clear whether the various question types carry any special pragmatic or rhetorical or conventional effects beyond those mentioned here, like the old "expects the answer "yes"", for example.

I can see how using such a question "as one of disbelief", as jan Tepan mentions, could work over using them a standard question forms especially in spoken toki pona for, as jan Kipo points out, doing so would require all speaking and listening parties understand how they work and how they sound (and in reality, does everyone speak toki pona exactly the same!?)

We don't know, since almost none of us have heard anyone else speak tp. But pretty surely not, even at the basic phonological level (listen to the various spoken specimens from people all over the world. They are generally hard to understand at first.

I am not sure about "as one of disbelief" though that is surely one possible use (though I would probably prefer 'a' or 'kin' to relying on just intonation.)